Have a 1991 GMC 1500 and the speedo works but the odometer does not - where do i start ? new part or relay or ?

SOURCE: Car speedo & odometer sometimes work OK, other times not at all.

Most likely a speed sensor is going bad (most cars and truck do not use mechanical speedometer cables anymore) most sensors are located near the differential in rwd cars or near the drive shaft on the transmission. Best bet is to get a Haynes manual for your car to help locate the speed sensor. Remove it and take it to the auto parts store so you can visually compare it to the replacement. Install the new speed sensor and it should restore your speedometer and odometer.

SOURCE: 1991 Dodge Daytona Speedometer and Odometer not working.

I had the same problem with my 90 daytona. The tach and the speedometer would work intermitantly. I took the whole gauge cluster out, and heated all the soldering with a solder gun to reflow the connections. It seems that this is a common problem with the connections cracking. You may not be able to see the cracks in the solder.

SOURCE: Speedo stopped working and tranny wont shift out of first!

I will try and clear up any confusion about the different model designations.The trans was first introduced as the Turbo Hydramatic 700 r 4.Later in the evolution of that family,it had improvements made on it by the factory engineers,and they redesignated it the 4L60 model.The 700/4L60 uses a throttle valve cable as a mechanical indication of the throttle position....to the trans.The TV cable regulates mainline hydraulic pressure inside the transmission.This model also uses a governor as a road speed mechanism.It is responsible for the TIMING of the upshifts,and is responsible for the trans being in first (low) gear from a standing start.In 1993,the 4L60E was introduced to the lineup.Same trans as the 700/4L60,but now it is totally electronic,and totally controlled by the PCM (Powertrain Control Module) based on electrical inputs/outputs from the trans,throttle position sensor,road speed,etc.The engineers took the 700/4L60 and did away with the governor and TV cable,made it totally electronic.Early 700's had a mechanically driven speedometer,while the later 4L60's and E's had an electronic speedometer.1993 was a transition year.I have seen both,the 4L60 and the 4L60E in 1993 model trucks,it depends on the month of the manufacture of the vehicle.Your truck could have either,or.The way to visually identify the difference is........on the driver side,the 700/4L60 trans case will have a round,black,governor cover,about 3 or 4 inches in diameter.The 4L60E case does not.The 700/4L60 also has the TV cable mounted on the passenger side of the trans case,and it routes up to the throttle body/gas pedal/accelerator linkage.The 4L60E does not.Recently,the 4L65E and 4L70E versions have been put into production.Based on your description of the malfunction symptoms,i would be inclined to say yours is probably the 4L60E version,because the speedometer malfunction occuring at exactly the same time as the shift malfunction.On a 700/4L60,the speedo malfunction would have no affect on the upshifts,the trans would operate normally.On the 4L60E,a speedo malfunction would likely cause no upshifts.You should still visually verify by the governor cover,or lack thereof,on the side of the trans case.It could just be a speed sensor malfunction if it has the "E" model.If so,it would have set a trouble code which can be accessed with a scan tool or a code reader.Hope this eliminates any confusion.Good luck!!

SOURCE: Ford Escort Odometer Not Working

these can also be caused by a bad alternator

SOURCE: 1991 crysler lebaron odometer not working speedometer is o.k.

Check the vehicle speed sensor in the transmission.